1. Technical Field
The present invention relates to a projection system suitable to be incorporated into a projector that enlarges and projects an image on an image display device and further relates to a projector.
2. Related Art
As a projector and a projection system suitable to be incorporated into a projector, for example, there is a known projector and projection system that use a fixed lens section, a movable lens section, and a concave mirror to reduce inclination of an oblique light flux in oblique projection with respect to the optical axis in order to perform wide-angle projection over a short distance (short-throw projection) while effectively preventing an image-forming light flux from being truncated by a lens barrel (see JP-A-2011-85922).
In general, in a projector, to prevent the screen-side image plane from inclining due to variation in back focal distance (distance from panel surface to projection system), it is important to perform precise back focus adjustment. In particular, in short-throw projection, in which the image plane tends to greatly incline, it is important to perform back focus adjustment by adjustment of the position of a fixed-lens-section-side lens group including a rear lens of the projection system. In the back focus adjustment, rotary adjustment using, for example, a helicoid screw is typically employed, and the back focus adjustment is performed by rotation of the fixed lens section.
On the other hand, centering each lens is also important work because how well the centering is performed affects optical performance. In particular, centering an aspheric lens is very important work because how well the aspheric lens is centered greatly affects the optical performance.
In a projection system for a projector, a demand for high resolution and other factors force employment of an aspheric lens in some cases. In recent years, an aspheric lens is employed not only in a typical projector but also in a short-throw type projector, and it is also conceivable that in the projection system that forms part of a short-throw type projector, an aspheric lens is employed, for example, not only in a movable lens section but also in a fixed lens section, that is, a lens section used to perform back focus adjustment.
However, to perform the back focus adjustment by rotation of the fixed lens section as described above, when the rotating action is performed, it is not always easy to perform the centering in the fixed lens section along with the back focus adjustment.